The present invention relates to composite structural members such as panels, boards or beams which comprise hemp hurds.
Industrial hemp is a bast fibre plant similar to flax. Bast plants produce two types of fibres. The outer bast fibres run longitudinally along the perimeter of the stalk. Bast fibres are very strong in tension and are typically used in textile manufacture, cordage and specially papers. Hemp bast fibres have also been used in medium density fibreboard.
There is significant interest in producing non-wood lignocellulosic structural building material, particularly with a view to forest conservation and the utilization of a waste material. For example, cereal straw has been successfully incorporated into an oriented strand board (xe2x80x9cOSBxe2x80x9d) with strength characteristics which are similar to or better than wood OSB of similar thickness. A description of a method and apparatus of fabricating a cereal straw panel may be found in co-owned U.S. Pat. No. 5,932,038.
A significant portion of a hemp plant is the hurd, which is the core fibrous material in the stalk. The hurd has been dismissed as a potential structural material due to its short fibre length and its low density. It is only marginally suited for paper production. In hemp processing, it is considered a waste product with limited value mainly as an absorptive material. This is unfortunate because the hurd may make up 70 to 75% of the hemp plant stalk mass.
It is known to use hemp hurd material with a cementitious binder to make a bulk material that may be handled in a similar manner to cement in that it may be poured into a mould or troweled onto a surface. However, there is no disclosure in the prior art that teaches the use of hemp hurd fibre in a structural member such as a board, a panel or a beam.
The present invention is directed to methods of producing structural members comprising hemp hurd fibres and to such structural members themselves.
Accordingly, in one aspect of the invention, the invention comprises a method of forming a structural member comprising the steps of:
(a) processing a hemp plant to produce hurd which is substantially free of bast fibres;
(b) splitting the hurd longitudinally to produce hurd strands;
(c) adding binder to the hurd stands; and
(d) pressing the hurd strands into a desired shape and allowing the binder to set.
The hurd strands may comprise substantially elongate strands having a length greater than about 20 millimeters and aspect and slenderness ratios greater than about 3:1. Shorter strands having aspect and slenderness ratios as low as about 1:1 may have an application in producing thin-stiff panels of limited bending strength. The structural member may be a board, a panel or a beam.
The method may further comprise the step of orienting a majority of the hurd strands such that the hurd fibres are substantially parallel in the structural member. In one embodiment which emphasizes structural strength, the hurd strands may be pressed such that the structural density is greater than about 500 kilograms per cubic meter. In another embodiment which emphasizes insulative and sound absorptive properties, the hurd strands may be pressed such that the structural member density is less than about 350 kilograms per cubic meter.
In one embodiment, the hurd strands may be mixed with wood strands to produce a composite wood/hurd structural member.
In another aspect of the invention, the invention comprises a structural member comprising oriented hemp hurd strands and a resin wherein said member is substantially free of hemp bast strands.